This invention relates to measuring devices and more specifically to a portable device for measuring magnetic field strength.
Therapeutic magnetic stimulation of human nerve tissue has significant advantages over traditional direct electrical stimulation. Electrical stimulation requires that an electrically conductive gel or buffer solution be applied between the electrodes supplying current and the surface of the skin of the patient. Long term excitation of the nerves is often accompanied by skin irritation caused by current concentration at the electrode/skin interface.
By contrast, magnetic stimulation does not even require direct contact with the patient, because magnetic stimulation causes current to be induced in the target tissues. Rapidly changing magnetic fields induce electric fields in biological tissue; when properly oriented and of the correct magnitude, the magnetically induced electric field transfers charge directly into the nerve tissue. When the localized membrane potential inside the nerve rises to a certain level, the nerve "fires." An excellent device and method for the implementation of magnetic stimulation of nerve tissue is described in U.S. Pat. No. 5,725,471, entitled "Magnetic Nerve Stimulator for Exciting Peripheral Nerves" to Davey et al. (the same Davey as is the inventor of the present invention), the teachings of which are incorporated by reference herein.
While magnetic stimulation is safer and easier to administer than direct electrical stimulation, it is important that the stimulator device maintain the proper magnetic field strength. If the magnetic field strength is too low, the charge induced in the target nerves will be too low and the nerves will be understimulated. However, if the magnetic field generated by the device is too strong, then the charge induced in the target nerves will be too high and injury may result.